1. Field of the Invention
The present invention relates to phosphors and, more particularly, to yellow light emitting phosphors and light emitting device packages using the same.
2. Discussion of the Related Art
Light emitting diodes (LEDs) are next-generation light emitting devices capable of substituting for fluorescent lamps, which are the most commonly used existing normal luminaires.
LEDs have less power consumption than existing light sources and may be regarded as being eco-friendly because they do not include mercury unlike fluorescent lamps. In addition, LEDs have advantages including long lifespan and high response speed as compared to existing light sources.
These LEDs may be used in conjunction with phosphors that absorb light emitted from LEDs to emit various colors of light. These phosphors may usually emit yellow light, green light, and red light.
White LEDs are currently fabricated into a combination of LEDs that emit blue light and phosphors adapted to convert emission wavelengths. Expansion in the use range of white LEDs causes requirement of more efficient LEDs and, to this end, emission efficiency of phosphors needs to be improved. In addition, demand for LEDs having greater reliability is increasing.
While yttrium aluminum garnet (YAG) phosphors, which are oxide phosphors as disclosed in U.S. Pat. No. 5,998,925, are known as yellow phosphors used in LEDs, the YAG phosphors have low thermal stability, which may problematically cause luminance deterioration and color coordinate variation at a high temperature.
In addition, while oxide phosphors and silicate-based phosphors are known as yellow and green phosphors, these phosphors have relatively low thermal stability and poor water resistance, thus being likely to have a negative effect on reliability of LED packages.
Therefore, there is a need to develop highly efficient and reliable phosphors capable of creating white light in cooperation with LEDs.
Moreover, blue LEDs may exhibit a wavelength shift to a shorter wavelength as output of the blue LEDs becomes higher and, therefore, there is a need to develop yellow light emitting phosphors that exhibit high excitation efficiency even at short wavelengths.